Dynamic modeling of the transition from passive to active rifting, application to the Pannonian basin

We examine a number of first-order features of Pannonian basin evolution in terms of the feedback relation between passive far-field-induced extension and active Raleigh Taylor instable upwelling of the asthenosphere. We show that active mantle upwelling following a phase of passive extension are viable mechanisms explaining the Pannonian basin formation. The dynamic interplay between far-field-driven passive extension and active thinning of the mantle lithosphere by convective upwelling beneath the rift zone is modeled using thermomechanical finite element methods. Our modeling results predict a first phase of passive lithospheric thinning which is followed by a second phase of late synrift to postrift active mantle lithosphere thinning due to buoyancy-induced flow beneath the rift zone. We argue that the pattern of coeval extension in the thinning region and compression in the flanking regions may be explained by the buoyancy forces due to lithosphere thinning. It is demonstrated that timescales of and stresses generated by both processes are comparable. The model appears also to explain the occurence of late shallow mantle-related decompression melts in the Pannonian region and late regional doming.